The Spin-dependent Scattering of Boosted Dark Matter

Boosted dark matter provides a promising approach to probe the light dark matter, whose computational framework in the spin-independent scattering process is well developed. However, the spin-dependent one lacks a unified treatment. The novelty of this paper is to give the first comprehensive derivation of the cross-section for boosted dark matter in spin-dependent scattering. When the transfer momentum is sufficiently large, there is a sizable enhancement to the proton structure factor from the time component. Besides, we find a residue momentum dependence in the quark-nucleon matching procedure, even without a light mediator. Such behavior can enhance the sensitivity compared with conventional contact interaction. We promote this endeavor by deriving direct limits on sub-GeV spin-dependent boosted dark matter through terrestrial data. The numerical results of the boosted structure factor and the non-relativistic structure factor are given explicitly in the paper and it shows that the excluded region of the boosted structure factor is about six orders larger than the non-relativistic structure factor.